<html>
<head>
</head>
<body>
<form name='formu'>

debut : <? echo "$jour_debut";?> <input type='text' name='date_debut'><input type='button' value='...' onClick="window.open('calendrier.php?form=formu&elem=date_debut','Calendrier','width=200,height=220')">
<br>
Fin : <? echo "$jour_fin";?> <input type='text' name='date_fin'><input type='button' value='...' onClick="window.open('calendrier.php?form=formu&elem=date_fin','Calendrier','width=200,height=220')">
</form>
</body>
</html>